This invention relates to positive displacement pumps, and more particularly, to positive displacement pumps having either three or four pistons or plungers, which are commonly referred to as triplex and quadruplex pumps respectively.
The present invention arranges the pump pistons so that they are equally phased, i.e., 120.degree. apart in the case of the triplex and phased 90.degree. for the quadruplex pump, and impart a motion or displacement to the pistons from a drive end so that the average velocity, i.e., speed with direction, of all pistons in the particular pump is equal to zero at all times. The output flow rate resulting from this arrangement is theoretically constant, as is the input or suction flow rate. Accumulators, which were utilized with prior pumps as a means of dampening the output pulsations inherent therewith, are not needed with pumps of the present invention. Longer suction lines are also possible and charge pressure arrangements are not needed because the inlet flow is also constant, thereby eliminating the acceleration head phenomenon resulting from start and stop inlet flow always encountered with prior art pumps.